If you run the session in the time stamp mode then automatically session log out will not overwrite the current session log.
Go to Session Properties –> Config Object –> Log Options
Select the properties as follows:
Save session log by –> SessionRuns
Save session log for these runs –> Change the number that you want to save the number of log files (Default is 0)
If you want to save all of the log files created by every run, and then select the option Save session log for these runs –> Session TimeStamp
You can find these properties in the session/workflow Properties.